Bacteria: Friends and Foes

Bacteria: More Than Just Germs

The Beneficial Roles of Bacteria

  • Contrary to popular belief, most bacteria are not harmful and many are beneficial.
  • Humans rely on bacteria for:
    • Fertilizing fields.
    • Recycling nutrients.
    • Protecting the body.
    • Producing food and medicines.

Nutrient Cycling and Decomposers

  • Nutrients are recycled in ecosystems.
  • Decomposers (detritivores or saprobes) obtain energy from dead organisms.
  • Decomposers return vital nutrients to the environment.
  • Without nutrient recycling, the raw materials necessary for life would be exhausted.

Nitrogen Fixation

  • All life forms require nitrogen, a key component of amino acids (the building blocks of proteins), DNA, and RNA.
  • Most of Earth's nitrogen is in the atmosphere as nitrogen gas.
  • Nitrogen Fixation: Certain bacteria convert nitrogen gas into nitrogen compounds.
    • These bacteria possess enzymes for nitrogen fixation.
    • Some live freely in the soil.
    • Others form symbiotic relationships with plant roots (e.g., soybeans, clover, alfalfa).
    • The bacteria provide usable nitrogen to the plant, enabling the plant to uptake ammonia and other nitrogen forms from the soil.
    • Plants at the base of the food chain obtain nitrogen, which is then passed to other organisms that consume them.

The Significance of Nitrogen Fixation

  • Without nitrogen fixation, far more fertilizer would be needed for growing plants.

Normal Flora: Our Microscopic Inhabitants

  • The human body is covered in bacteria, both internally and externally.
  • Most of these bacteria are harmless and are referred to as normal flora.
  • Function of normal flora: competitively exclude harmful bacteria, preventing them from colonizing and causing disease.

Escherichia Coli (E. Coli): A Dual Role

  • E. coli resides in the intestines. Certain strains may cause food poisoning.
  • Harmless E. coli strains in the digestive tract of humans and other mammals:
    • Synthesizes vitamin K, which is crucial for blood clotting.
    • E. coli benefits by obtaining a warm environment and food, while humans benefit from the produced vitamin K.

Bacteria in Food Production

  • Bacteria are essential in the production of various foods, including:
    • Cheese
    • Yogurt
    • Buttermilk
    • Pickles
    • Chocolate (bacteria break down the covering of cocoa beans)

Bacteria in Medicine and Research

  • Bacteria are used in the commercial production of vitamins (e.g., vitamin B12, riboflavin).
  • Antibiotics originally derived from bacteria:
    • Streptomycin
    • Bacitracin
    • Tetracycline
    • Vancomycin

Pathogenic Bacteria and Disease Mechanisms

  • Only a small percentage of bacteria cause disease.
  • Disease mechanisms:
    • Rapid multiplication at the site of infection overwhelms the body's defenses.
    • Secretion of toxins or other harmful substances.
      • Botulism: Bacteria secrete a toxin that paralyzes cells in the nervous system.
      • Cavities: Bacteria use sugar in the mouth to produce acids that erode teeth.

Bacterial Diseases in Plants

  • Bacteria can infect plants, leading to crop destruction and ecological consequences.
    • Citrus canker: A bacterial disease affecting orange trees, impacting the Florida citrus crop and resulting in eradication programs.